An engine of vehicle is installed in an engine room of a vehicle body through an engine mount so as to isolate and dampen vibration of an engine. A rubber mount that isolates and dampens the vibration through an elastic force of the rubber, and a hydraulic engine mount (fluid-filled type engine mount) in which a predetermined amount of hydraulic fluid is sealed, has been widely used for a passenger vehicle.
The hydraulic engine mount has a structure in which a predetermined amount of hydraulic-fluid is sealed therein to dampen the vibration in accordance with flow of the hydraulic-fluid, and has an effect of attenuating vibration simultaneously in a high frequency range and a low frequency range. Therefore, an application range of the hydraulic engine mount has been increased.
The hydraulic engine mount includes a case and an insulator and a diaphragm, wherein the insulator and diaphragm are coupled to an upper end portion and a lower end portion, respectively, inside of the case. The inner space of the case is divided into an upper fluid chamber and a lower fluid chamber by a nozzle plate.
In general, the nozzle plate is formed such that an upper nozzle plate and a lower nozzle plate are coupled to each other. In the center of the lower nozzle plate, a lower center hole is formed and an annular flow channel is formed along the outside of the circumference of the lower center hole. One end of the flow channel is communicated with the lower fluid chamber.
The upper nozzle plate is placed in the upper side of the lower nozzle plate. The upper nozzle plate includes an upper center hole formed in the center of the upper nozzle plate and a hole configured to allow the other end of the flow channel to communicate with the upper fluid chamber.
Since the upper fluid chamber and the lower fluid chamber communicate with the flow channel, the hydraulic fluid of the upper fluid chamber and the lower fluid chamber flows through the flow channel.
The flow of the hydraulic fluid through the flow channel is performed as an internal volume of the upper fluid chamber is increased or decreased when the insulator is elastically deformed by the load movement and vibration transmitted from the engine. In order to improve vibration characteristics and damping performance, a membrane may be mounted between the upper nozzle plate and the lower nozzle plate.
An edge of the lower surface of the membrane is fitted to the upper surface of the lower nozzle plate and an edge of the upper surface of the membrane is fitted to the lower surface of the upper nozzle plate.
An edge portion where the membrane and the lower nozzle plate are engaged with each other and an edge portion where the membrane and the upper nozzle plate are engaged with each other are apart from each other by a predetermined distance so that the hydraulic fluid of the upper fluid chamber and the lower fluid chamber can flow.
When idling, the hydraulic fluid flows around the edge of the membrane to lower its dynamic characteristics. The hydraulic fluid perform a damping function by flowing through only the flow channel when the large displacement.
However, excessive vibration of the membrane due to a clearance formed at the coupling portion of the membrane causes noise. Such the noise can be eliminated by reducing or eliminating the clearance. However, when the clearance is reduced or eliminated, the dynamic characteristics may be increased and Noise, Vibration, and Harshness (NVH) performance may be reduced.